The History of Domestic Water Heating
In the beginning, there was cold water-and people didn't bathe much. They masked body odor with perfumes and oils or just went around smelly. Even as recently as the turn of the century, running hot water was a luxury. It was available only to those who were well off. In the United States today, a personal supply of hot water is thought of as a necessity, right up there with food and shelter. (Just try going without it.)
Over time, people have heated water in many ways. A brief look at some of these methods offers an interesting perspective and demonstrates how some of these older and now unused techniques could have applications today.
From stove to storage tankWhen wood and coal were the prevalent fuels, water was usually heated in a pot over the fire or in a kettle over the cooking stove. Some stoves had a reservoir lined with tin, copper or porcelain. This would be filled with water for heating. Heating enough water for a bath was a time-consuming ordeal. Much of Saturday was spent getting cleaned up for church on Sunday.
Later, when running water came indoors, a chamber or pipe loop called a water-back (or a water-front) was installed in the fire box of the stove. Heated water would move by convection through this chamber to a storage tank. (For reasons that can only be guessed at, these tanks were called range boilers, even though it was the stove that did the heating.) Some of these old systems are still operating out there today. The oldest water-back/range boiler we've seen still hooked up and in use dates back to the early 1920s.
A variation of the stove/storage tank idea was the "scuttle-a-day" heater, which used coal. This was a small cast-iron device. Short and squat, with a rounded top, it looks more like Star Wars' R2-D2 than a water heater. Hooked up to a storage tank in the same way as the water-back, it used one scuttle (bucket) of coal per day to keep the water hot-at least relatively hot. Using the scuttle-a-day eliminated the need to fire up the kitchen stove when hot water was needed. It saved fuel and avoided turning the house into a sauna during hot weather. This heater had damper controls to adjust the rate of burning, but fully automatic water heating was yet to come.
Another interesting type of heater was the side-arm. It usually had a gas burner placed underneath a copper coil. These were "holstered" in a cast-iron shell. Water would be heated in the coil, and then convection would drive the heated water to a storage tank, just as it did in the water-back and scuttle-a-day coal burner.
Originally, side-arm heaters simply had a gas valve that was operated by hand. The gas was lit with a match when you wanted a bath. Forgetting to shut it off when done with the bath "triggered" a potentially explosive situation. Later, automatic controls and safeties were developed that made the side-arm heaters easier to live with. One advantage of the side-arm heater was that if its storage tank rusted out, you could simply replace that one component. You'd transfer the burner and other pieces to your new tank, keeping costs down. Planned obsolescence had not yet become a way of life.
It's interesting to note that one of the most efficient water heaters available today, the Marathon, is an updated side-arm heater. One of the main reasons it is so efficient is that the burner is separated from the storage tank. Because there is no flue running up through the stored hot water, standby heat loss from the tank is greatly reduced.
Hot water in an instantUntil the 1890s, all forms of water heating both heated and stored the water. But gases provided another option. Kerosene, gasoline and a variety of gases have been used to heat water. Some gases, such as acetylene and producers gas, could even be made on site. With the advent of high-energy liquid and gaseous fuels, instantaneous heating became possible. These fuels were much easier to regulate automatically than wood or coal.
The bath heater was one of the first instantaneous types. We find one variety particularly interesting (see illustration). Once a pilot was lit, turning on the water would also turn on the gas burner. Water flowed up through a pipe to a sprinkler inside the top of the unit. As water sprayed out through the combustion gases, it collected heat (and combustion by-products). From there the water cascaded over metal that was being heated by a flame, collecting more heat. The water then traveled around to a spigot and into the tub.
Ad copy in Sweet's Catalog (1906) boasted that this method utilized "92 heat units out of a possible 100, a feat never before accomplished in heater construction." This heater was extremely efficient, though it did result in slightly tainted bath water. (Perhaps the somewhat acidic water cleaned better.) Today, the most efficient furnaces and boilers also condense flue gases.
As the century turnedAt present, four or five manufacturers produce most of the water heaters in the United States. In the early part of this century, there were more than 150 manufacturers. Many types of heaters were competing for business. The two major camps were automatic instantaneous and automatic storage heaters. You already know which prevailed.
It may have to do with how people bathe. For many reasons, precise temperature control has always been difficult with instantaneous heaters. That didn't matter when filling a tub, which is what most people used to do. As toes tested the water, hot or cold was added until the bather was satisfied. When the "rain bath" or shower became more common, if the water temperature fluctuated, it was noticed-and not much appreciated. Tank-type heaters seemed to gain in popularity around this time.
Galvanized steel tanks were common, but longer-lasting copper, bronze and monel (similar to stainless steel) were also available. Performance was improved dramatically when insulation was added to the tank. (Surprise! What seems obvious to us now was innovation then.) Like the side-arm heater, some of the early tank-type heaters were designed so you could replace just the tank and reuse the rest of the components, even the insulation.
Because tankless heaters could produce hot water as soon as the pilot was lit, we imagine tank-type heater makers felt at a competitive disadvantage. They came up with some innovative ways of getting hot water from a tank within a few minutes after heating had begun.
One method placed a coil of pipe in the combustion chamber. Water was fed into the coil from the bottom of the heater. A tube ran from the coil up the flue and connected to the hot outlet pipe. Water was heated in the coil almost immediately; it could either be used right then or go to storage.
Another method wrapped a jacket about an inch away from and completely around the flue, surrounding it inside the tank. This jacket was open both top and bottom, creating a rising current of heated water. Like the previous method, hot water-although limited in quantity-was almost instantly available for use.
These tank heaters still took just as long as ever to heat their entire contents, but they could provide small amounts of hot water quickly for chores. That meant the heater could be turned on briefly and then kept off most of the time, greatly cutting standby heat losses.
Early solarSolar water heating started catching on around the turn of the century. Originally there were batch heaters, now called internal collector and storage (ICS) units. These heaters had one or more tanks placed behind glass, in an enclosed box. They are very simple, with no moving parts and little risk of freeze damage. Their main drawback is substantial overnight heat loss.
Thermosyphon systems were an improvement. This method placed the tank above the collector and used convection to move heated water into the tank (just like the side-arm heater). One manufacturer was Day and Night, so called because their heaters provided hot water both day and night. Their insulated tanks kept stored water hot after the sun went down, and that was a solar first.
The company suffered when unusually cold weather caused freeze damage to many of their collectors. Their remedy was to install a heat exchanger between the tank and collector and fill the collector with alcohol and water. (We personally feel that was one of the most elegantly simple and efficient solar systems ever devised.)
A second problem occurred as solar tanks aged and began to leak. A major cause of leaks then, as now, was using different metals together in water. When metals are mixed in this way, one of them always corrodes to protect the other. One metal turns bodyguard to the more "noble" metal, and it sacrifices itself. Thus, steel rusts away to protect copper. When these metals were used together, plumbing corroded and holes developed. Water leaked out and caused havoc. Today, plastic-lined steel nipples and dielectric unions can be used effectively to separate the metals and prevent this problem.
These solar tanks were usually installed in attics, up under the peak (so thermosyphoning with the roof-mounted solar panels could work). When tanks leaked, it was always a major headache. Even if they had not been packed in boxes with cork bits all around, access to attic tanks was difficult. Replacement would have been a nightmare, and it was probably seldom attempted. Instead, tanks or their plumbing failed, houses flooded, and solar developed a black eye. (If only solar system owners had been informed about galvanic corrosion and the use of sacrificial anodes to protect their tanks.)
At this time, gas was becoming more widely available, and its price was very attractive. Utility companies even got into the business of selling water heaters (free bath towels included) to build demand for their product. Solar was not able to compete against low gas prices or the freedom from involvement that abundant utility energy offered. Solar water heating slowly disappeared.
Tank evolutionIn the meantime, tank-type heaters had become dominant. Various methods and energy sources existed, but electric and gas tank-type heaters took over the lion's share of the market. Tank-building technology was changing, and some interesting things happened. As gas prices started going up, attempts were made to make tanks more efficient.
One such tank was the "U" tube heater. It's enlightening to compare it to present-day heaters. Modern gas heaters have a flue, usually a 3- or 4-inch diameter pipe running from the combustion chamber right up through the center of the tank. This flue vents combustion fumes. However, it also acts like a chimney, and heated air is constantly flowing up and out. This is all lost heat.
In the "U" tube heater (see illustration), the flue went up, inside the tank, until it got near the top. Then it made a 180-degree turn and headed back down. It exited near the bottom and connected to an external vent pipe. This inverted U created a heat trap. It would vent only when the burner fired, so it lost much less heat. Also, because the U doubled the surface area of the pipe inside the tank, more heat was captured by the water. It was very efficient.
Another design variation was the slow-recovery heater. It fired at 5,000 or 10,000 BTUs per hour instead of the 30,000 to 40,000 BTUs modern or "fast-recovery" heaters burn. Therefore, the flue's outlet could be smaller. This resulted in more efficient capture of heat during combustion and less heat loss during standby periods.
Another change in manufacturing was the advent of glass lining. This glass coating is similar to ceramic glazing. Baked onto the inside of a steel tank, it provides a very good defense against rusting. Because a perfect process for glass lining tanks has yet to be developed, sacrificial anode rods are used to protect the steel at any "holidays" or imperfections in the lining.
This system worked so well that manufacturers eventually stopped making tanks of expensive metals such as copper and monel. Instead, their better tanks were made of extra-heavy steel lined with a double coating of glass. With such good protection and thick steel, a tank could last decades after its anode was used up. In fact, we recently ran across a 42-year-old heater that is still in good condition.
As the business of making and selling water heaters grew ever more competitive, people found ways to cut costs. Tank quality began to deteriorate as tanks were made of thinner steel, and double glass lining was no longer offered. Metal drains were replaced with plastic.
Experience has shown us that modern tanks are more delicate than their predecessors, but with maintenance, their service lives can be greatly extended. More expensive tanks today may have a second anode, or they may have a plastic lining or be entirely plastic to prevent corrosion. Still, glass-lined units make up the great majority of tanks in service and sold today.
Safety and energy upgradesEfforts have been ongoing to make water heaters safer. The results have been so successful that at one point, it was suggested we didn't need to install relief valves any more because tanks had quit blowing up. Tanks do explode less often today, precisely because relief valves do get installed and because heaters have better controls.
Manufacturers have also been fine-tuning heaters for better energy performance to meet stringent federal energy codes. This has pros and cons. Yes, plastic drain valves lose less heat than brass ones, but very often they simply don't work. Yes, some small amount of heat is lost through an anode's exposed hex head. However, proposals to insulate and cover the hex head may do more damage than good. Unless they specify that access to the anode remain, anode replacement and water heater maintenance will become much more difficult.
One area that is likely to get even more attention in the future of water heating is conservation. Once the heaters themselves have been tweaked for every BTU of performance, it will make sense to zero in on the antiquated distribution systems where many of those BTUs are being lost. Other areas for improvement include heat recovery and reducing consumption of hot water.
Because they work so well, water heaters are generally the least thought-about piece of equipment in most homes. But it's useful to take the time to understand them, learn a little about their past and guess at their future. That way we're in a good position to do what's needed to get the best performance and longest life from our water heating systems. It's the best way to stay in hot water.
Further recommended reading: A GOLDEN THREAD: 2500 Years of Solar Architecture and Technology, by Ken Butti and John Perlin. Currently out of print, but check in used bookstores or the library.
This article originally appeared in Home Power Magazine, August/September 1995. 916-475-3179